Maize chlorotic dwarf (virus) Control Methodss Resistant varietys Control Johnsongrass
Northern corn leaf blight (fungus) Symptom/Signs Gray green elliptical (cigar-shaped) spots, 2-6 inches long on hybrids with no resistance.s Lesion size can be affected by hybrid.s Can be confused sometimes with Stewart’s wilt if certain resistance genes are present.
Southern corn leaf blight (fungus) Symptom/Signs Spots on leaf smaller and more numerous than Northern corn leaf blights Spots vary in size and shape due to the genetic background of the hybrid.s Common race “O” produces tan, elongated spots between the veins that have limited parallel margins and possibly buff to brown borders.
Carbonum(Northern corn) Leaf Spot (fungus) Symptom/Signs Race 3 produces very narrow spots often resembling “beads on a string”.s Lesion (spot) type varies with the hybrids Often spreads after leaf tissue matures
Carbonum(Northern corn) Leaf Spot Conditions favoring developments Moderate temperatures and high humiditys Spores are abundantly produced on old spots on mature leavess Minor importance, small impact on yield.
Gray leaf spot (fungus) Symptom/Signs Rectangular lesions with sharp parallel edges, restricted by veins with yellow margins Window pane look, and old lesions are opaque.s Early lesions are small necrotic spots with chlorotic halos.s Often symptoms are worse along the edges of fields
Rust Conditions favoring developments Spores are wind blown from the south.s Moderate temperatures (61-80) and high humiditys Infections often occur in the whorl where moisture and humidity are high
Fusarium stalk rot (fungus) Conditions favoring developments Reduced tillage or no-tills Fungus overwinters in crop residues Warm, wet conditionss Can enter through wounds or directly ( corn borer interaction)s Same organism causing scab in cereals
Fusarium stalk rot (fungus) Control Methodss Hybrid selections Tillages Proper fertilitys Rotations Early harvest
Fusarium ear rot (fungus) Symptom/Signs White fungus growing on kernelss Pink discolorations “Starburst” symptom on infected kernels
Phytophthora root rot (fungus) Control Methodss Resistant varietys Seed treatments using Apron, Apron XL, or Allegiance control the damping- off stage.
Rhizoctonia root rot (fungus) Symptom/Signs Seedlings emerge and dies Brown, red-brown, or red sunken lesion on roots or base of the seedling stem.
Rhizoctonia root rot (fungus) Conditions favoring developments Cool, damp conditionss Fertility, soil conditions and the amount of fungus in the soil can all influence the degree of infection.
Rhizoctonia root rot (fungus) Control Methodss Fungicide seed treatmentss Later planting date
Septoria leaf spot (Brown spot) Symptom/Sign s Irregular dark brown spots on unifoliate leaves progressing to trifoliates later in the season. s Infected unifoliate leaves turn brown and drop s Black fruiting bodies (pycnidia) of the fungus form in old spots.
Septoria leaf spot Conditions favoring developments Fungus overwinters on old infected plant debriss Unifoliate infection provides inoculum for later infections Warm, wet weather conditions especially later in the season influences brown spot in the canopy.
Septoria leaf spot Control Methodss Rotations Plant less susceptible varietiess Plow under crop residues
Charcoal rot Symptom/Signs Usually after midseason, plants appear stunted in irregular areas of the field.s Leaves may turn yellow and wilts Lower stem and taproot develop a gray to silvery discolorations Microsclerotia develop in epidermis on root and lower stem and inside pith resembling charcoal dust
Charcoal rot Conditions favoring developments Low soil fertilitys Continuous cropping of soybeans.s Low soil moisture and hot temperatures increase disease severity.
Charcoal rot Control Methodss Plant later maturing varieties late group IV’s and group V’s.s Rotate with small grains, corn and sorghum for at least 3 years in severely infected fields.s Do not overplant, causes seedling stresss Good fertility practices
Sclerotinia white mold (fungus) Symptom/Signs Wilting and death of the upper leaves of the plants during early pod developments Often occurs in patches in low areass White mat of fungus on stem at nodes often seens Stem lesions often girldle the stem and the uper portions die and produce no pods.s Large sclerotia on stem and sometimes in pith
Sclerotinia white mold (fungus) Conditions favoring developments Cool, wet conditions that favor germination of sclerotia within the upper 2 inches of soil.s Narrow row spacings Dense canopy structures Fields with history of white mold on crops of peas, beans, and soybean
Sclerotinia white mold (fungus) Control Methodss Avoid planting soybeans after other susceptible crops such a peas, snap and lima beans, and sunflowers.s Choose varieties that are shorter, more open
Pod and stem blight (fungus) Symptom/Signs Rows of black fruiting bodies (pycnidia) on stems, petioles and pods late in seasons Infected seeds are decayed which leads to direct yield loss
Pod and stem blight (fungus) Conditions favoring developments Disease of senescing soybeanss Seed infection favored by delayed harvests Warm, rainy weather during pod development through maturity.s Low potash levels favor more seed infection.
Pod and stem blight (fungus) Control Methodss Rotations Tillages Resistant varietys Maintain high level of potash fertility
Anthracnose Symptom/Signs Often appears in early reproductive stages on stems, petioles and pods as an irregularly shaped brown areas. Often resembles pod and stem blight.s Fruiting bodies of the fungus are randomly scattered on infected plants tissues and produce black spines called setae that can be seen.s Can produce cankers on petioles and stems causing severe defoliation.
Anthracnose Conditions favoring developments Overwinters on debris and can infect seed.s Moist, warm weather during reproductive stages.s Plants are most susceptible from bloom to pod fills Need wet periods of 12 hours or more for infecton to occur.
Anthracnose Control Methodss Plant disease free seeds Plow down old soybean residuess Rotation
Soybean cyst nematode Symptom/Signs Stunted yellow plants in patches or large areass Poorly developed rootss Suppressed nodulations Lemon shaped cysts (females) on roots.
Soybean mosaic (virus) Control Methodss Certified seeds Resistant variety
Tobacco Ringspot Virus Symptom/Signs Primarily seedborne at a low level in the fields This results in scattered infected plants.s Maturity is delayed so they remain green until killed by frosts Pods are underdeveloped, tops of plants have shortened internodes, and leaves are distorted
Tobacco Ringspot Conditions favoring developments Nearby crops that may harbor the viruss Insect vectors are possible and disease is often found near the edges of fields.s Dagger nematode (Xiphinema) may cause a low level of transmission.
Tobacco Ringspot Control Methodss Planting virus free seed.
Powdery Mildew (fungus) Symptom/Signs Irregular shaped yellow areas on leaf initaillys White powdery mass of fungus on upper surface of lower leavess Older PM colonies will have small brown to black sexual fruiting structures present late in the spring
Powdery Mildew (fungus) Conditions favoring developments Optimal powdery mildew development occurs between 60- 72 F basically cool, wet conditionss High nitrogen fertilitys Dense stands of susceptible varietiess High humidity
Powdery Mildew (fungus) Control Methodss Resistant varietiess Rotation is of some value but limiteds Balanced fertilitys Fungicides (seed and/or foliar treatments)
Leaf rust (fungus) Symptom/Signs Orange-red pustules mostly on upper leaf surfacess Randomly scattered within the canopys Usually appears after heading
Leaf rust (fungus) Conditions favoring developments Temperatures from 59-72 F and free- moisture. Needs adequate rainfall.s Overwinters far souths Spores carried by wind
Leaf rust (fungus) Control Methodss Resistances Fungicides
Septoria leaf and glume blotch (fungus) Septoria nodorum Symptom/Signs Elongate lens-shaped lesions with yellow marginss Black fruiting bodies in center of lesion help distinguish from tan spot. Often found in orderly rows.s On the heads a brown to gray -brown discoloration occurs and pycnidia are found on the infected glumes
Septoria leaf and glume blotch (fungus) Conditions favoring developments Optimal development is between 68-82 F wet, windy conditions.s Minimal wet periods of 6 hours, but mostly needs 16 hours of wetness.
Septoria leaf and glume blotch (fungus) Control Methodss Fungicidess Tillage
Scab (fungus) Symptom/Signs Bleached spikelets on part or all of wheat heads Pink or orange spore masses may be seen at the base of infected spikelets during periods of high humiditys Infected heads are sterile or contain white shriveled grains Same as Fusarium on corn (mycotoxins)
Scab (fungus) Conditions favoring developments Spores from corn, wheat and grass residue spread to flowering wheat under warm, wet conditions.s Temperatures between 77-86 F and continous moisture at flowering are most favorable for epidemics.
Scab (fungus) Control Methodss Tillage prior to plantings Rotation (limited value in areas with intense no-till or reduced tillage corn production)s No resistance
Take-all (fungus) Symptom/Signs Infected plants are stunted and ripen prematurelys Best identified at heading by stunted growth in patches and heads are bleached white and often steriles Black lesions at base of crown under the lowest leaf sheaths Plants pull easily from the soil from extensive rot rot.
Take-all (fungus) Conditions favoring developments Continuous wheat productions High pH, poorly drained soils or wet years
Take-all (fungus) Control Methodss Rotations Maintain good fertility levelss No good resistant varietiess Control grassy weeds before cropping to wheat
Barley yellow dwarf (virus) Symptom/Signs Ambiguous often look like nutritional disorderss Fall infection results in patches of yellow, stunted plants. Spring infections usually result in plants of varying heights and yellow or purple colored flag leaves after head emergences Occurs in patches of field where aphid vectors feed
Barley yellow dwarf (virus) Conditions favoring developments Transmitted by aphidss Cool, moist conditions (50-65 F)s Early planted fields attractive to aphidss Mild winter with aphids
Barley yellow dwarf (virus) Control Methodss Tolerances Later planting dates Control aphids
Wheat spindle streak mosaic (virus) Symptom/Signs Non-distinct yellow streaks can be confused with early stage powdery mildews Often produces yellow-green mottling, dashes and streaks. The streaks often have tapered ends forming spindles.s Entire field affected--not patchy. Low spots in field can have more severe symptoms.
Wheat spindle streak mosaic (virus) Conditions favoring developments Soil borne viruss Transmitted by fungus, in the fall.s Cool weather (46-53 F) produces the most symptomss “Disappears” as temperatures increase
Wheat spindle streak (virus) Control Methodss Resistant varietys Rotation of some values Later plantings Poultry manure may decrease disease incidence
Loose Smut (fungus) Symptom/Sign s Black smutted heads on wheat
Phytophthora root rot (fungus) Control Methodss Select well drained sitess Break up compacted soils to enhance drainages Plant resistance varietiess Use Apron seed treatments to avoid seedling damping-off
Anthracnose (fungus) Symptom/Signs Wilted stemss Diamond shaped lesions on lower stems Lesion gray with red margins Scattered in the fields Infected stems with characteristic diamond shaped lesion will also produce a typical shepard’s crook
Anthracnose (fungus) Conditions favoring developments Warm, humid conditionss Late summer/ early fall weather can be very favorable for infection
Anthracnose (fungus) Control Methodss Resistant varietys Clean harvesting equipment before first cutting and when going from a known infected fields to a healthy field.
Sclerotinia crown rot (fungus) Symptom/Signs Fall- planted alfalfa dies in spring during cool, wet conditions.s Cottony web-like growth on stems and crownss Stems turn brown, then soft and mushy then disintegrate.s Black fruiting bodies (Sclerotia) on stem
Spring blackstem (fungus) Conditions favoring developments Cool, moist early season and again in falls Heavy dew or rain
Spring blackstem (fungus) Control Methodss Early cuttings Plant moderately resistant cultivars
Verticillium wilt (fungus) Symptom/Signs Scattered infected stemss Early symptoms include V-shaped chlorosis at leaflet tipss Not all stems on the same plant infected initiallys Internal root tissue is often brown, but it is not a dependable diagnostic feature.
Verticillium wilt (fungus) Conditions favoring developments Introduced on seed usuallys Could be disseminated in manures Insects can can serve as vectorss Can spread within the field during cutting
Verticillium wilt (fungus) Control Methodss Plant clean seed free of debriss Plant resistant varietiess Disinfestation of cutter bars and equipment
Most Common Symptoms of Nematode InjuryField Symptomss Stunting and sometimes yellowing of plants in patches of varying sizes Not definitive, need to look at rootsPlant Symptoms and Signss Galls, cysts, lesions or dead areas on roots
FUNGICIDE CLASSIFICATIONs PROTECTANT – Forms a protective barrier on the plant surface that prevents spore germination eg. Dithane, Bravo, thirams SYSTEMIC – Moves in the plant from point of application across the leaf or into new growth. Can move from roots to above ground parts. Prevents spores from germinating or kills them soon after germination. Eg. Tilt, Baytan, Raxil, Quadris, Ridomil.s ERADICATIVE (Curative)- kills fungus already present. Some systemic fungicides have some curative activity
TREATMENT THRESHOLDS FOR FUNGICIDE APPLICATIONs Thresholds are available for making spray decisions for wheat in the mid-Atlantic region.s Use stage of development and amount of disease present to determine need for an application.